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BULLETIN 




Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chi< 
September 19, 1913. 



THE AGRICULTURAL UTILIZATION OF ACID LANDS 
BY MEANS OF ACID-TOLERANT CROPS. 

P.y FBEDEBICK V. Coville, 

Botanist in Charge of Economic and Systematic Botany. 
INTRODUCTION. 

In the past 20 years farmers have witnessed tin 1 development of 
what may he called a lime-and-clover literature and the growth of a 
corresponding agricultural practice. The scientific researches of 
various investigators published from 1867 to 1888 had demon- 
strated that leguminous plants through the bacteria of their roof 
tubercles were able to take nitrogen from the atmosphere and that 
when a crop of these plants was plowed under the land was enriched 
as if by a corresponding application of manure. 

In the northeastern United States the principal leguminous plant 
used in crop rotations had been red clover. The scientific con- 
firmation of the popular belief that this plant had high value as a 
green manure greatly stimulated its use. the customary procedure 
being to plow under the clover turf after taking off one or two cut- 
tings for hay. It was found, however, that if the land is acid in 
its chemical reaction red clover make- but feeble growth. If the 
chemical reaction i- neutral or slightly alkaline and other condition- 
are favorable, heavy crops of red clover are produced. This con- 
sideration greatly extended the practice of applying lime, in order 
to neutralize the acidity of the soil and thus increase the inanurial 
use of clover in crop rotations, over large areas of the older lands 
of the eastern United States. 

It was found also that timothy, the chief hay grass of this region, 
was much longer lived and more productive in acid land when limed, 
and that wheat, one of the principal cereals, yielded much more 
heavily when treated in the same manner. Within the la-t few 
years the attempt in the acid Mast to cultivate alfalfa, the great hay 
crop of the alkaline West, has conveyed the same lesson in a still 
more striking manner, for alfalfa can not be grown satisfactorily in 
any soil, however fertile, which has an acid reaction. When grown 

6133°— 13 






2 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 

in the eastern United States alfalfa is not successful, except on 
calcareous soils, unless the natural acidity of the soil has been neu- 
tralized by suitable applications of lime. 

One result of this advocacy of lime has been that in our anxiety 
to neutralize our acid soils and thus make them yield larger crops 
of such staples as clover, timothy, wheat, and alfalfa we have neg- 
lected to recognize clearly and to utilize the fact that some agri- 
cultural plants thrive as well in an acid soil as in an alkaline soil, 
or even better. It is proposed to discuss in this bulletin the bearing 
of soil acidity on agriculture and to direct attention to the utilization 
of part of our cheap acid lands through the development of rota- 
tions in which all the crops are acid tolerant, and the. cost of making 
frequent and heavy applications of lime is therefore eliminated. 
These considerations are especially pertinent in sections where lime 
is expensive because of the remoteness of good commercial deposits 
of limestone. Where lime is not expensive the use of applications 
sufficiently heavy to neutralize the acidity of the soil is unques- 
tionably profitable for many of the staple agricultural crops. 

SOURCE OF SOIL ACIDITY. 

One of the principal sources of soil acidity is decaying vegetation. 
The fallen leaves that carpet the floor of a forest are exceedingly 
acid. Freshly fallen leaves of some of our common trees show the 
following degrees of acidity, expressed in tons of ground limestone 
required per acre to neutralize a compact layer 6 inches in depth, 
estimated to weigh when dry 500,000 pounds, one-fourth as much as 
ordinary soil. 1 

Table I.— Acidity of freshly fallen leaves, in terms of lime requirement per uere. 



Kind of leaves. 


Acidity. 


Kind of leaves. 


Acidity. 


White oak 


row.v. 

25 
10 
22 


Sugar maple 


Tom. 

22 
14 






22 









It is well known to farmers that on newly cleared timberland, not 
burned over, most crops do not grow well at first. A few. however, 
thrive in such situations, notably rye, buckwheat, and potatoes. All 
these are known to be acid tolerant. Table I, although represent- 
ing conditions of acidity in excess of that actually existing in a 
cleared field, shows one of the sources of the acidity with which the 
plants have to contend and which is fatal to crops that are not acid 
tolerant. Another source of pronounced acidity in newly cleared 
timberlands is the freshly killed roots of the trees and underbrush. 



1 These acidity determinations were made by Mr. G. II. Baston, of the Bureau of Plant 
Industry, using phenolphthalein as an indicator, after boiling off the carbon dioxid. 



0. OF D, 
SEP 25 J913 



a. 
Co Zs* AGRICULTURAL UTILIZATION OF ACID LANDS. 3 

It is also well known to farmers that, after a few years' prelimi- 
nary culture in rye potatoes, and buckwheat, virgin timberland with 
its humus-laden soil of a century's accumulation from rotting leaves 
and roots will sometimes produce heavy crop- of timothy, wheat, and 
clover for one or two generations. The success of these crops shows 
that the soil has ceased to he acid. Again, when the -tore of humus 
derived from the forest lias finally been exhausted after long years 
of ceaseless cropping, these soils revert to a condition of acidity, when 
lime is regarded as necessary to further agricultural prosperity. 

What is this peculiarity of forest leaves by which they make the 
soil at one time acid, at another alkaline? Tt is worth while to con- 
sider this question, for its answer will throw new light on the prac- 
tice of agriculture. 

DECOMPOSITION OF LEAVES. 

A layer of freshly fallen leaves on bare ground, moistened by rain. 
begins at once to decompose. A brown liquid leaches out of the 
leaves into the underlying soil. This liquid is acid. If the soil itself 
is naturally acid, its acidity is increased by these teachings. If the 
soil is sand, neutral in chemical reaction, it is made acid by the 
leachings from the leaves. But if the soil is alkaline from the 
presence of carbonate of lime, as in the case of ordinary loam of 
high fertility, the acidity of the leaf water is neutralized and its 
brown matter is precipitated, forming a poll ion of the black humus 
of the soil. ( )n such an alkaline soil leaves decay rapidly from 
beneath and form a black, mellow, and very fertile leaf mold in 
which all traces of leaf structure have disappeared, ruder such con- 
ditions the layer of leaf litter is always thin, often not lasting 
through the summer, and the transition from leaves to underlying 
mold is abrupt. 

In -and. however, there i- no such acid-neutralizing substance, ami 
both soil and leaves remain in an acid condition unfavorable to 
complete decay. The next year a fresh fall of leaves brings :i new 
accession of acidity, and the acid condition of the leaf litter becomes 
permanent. In a sandy oak or pine woods there is thus built up a 
tough mat of upland peat often several inches in thickness, com 
posed of half-rotted leaves interlaced with the rootlet- of trees and 
underbrush. Such peal mats are always acid, like ordinary bog peat. 

One might conclude from what has been said that leaves unless 
treated with lime would remain acid throughout the process of 
decomposition. Such a conclusion, however, would be erroneous. 
Leaves when sufficiently decayed lo-e their acidity and of them- 
selves produce a black mold that is not merely neutral in reaction, 
but sometimes markedly alkaline. 



4 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 

CHANGE FROM ACIDITY TO ALKALINITY. 

The reason for this change from acidity to alkalinity lies primarily 
in the chemical composition of the leaves. From the beginning 
they are heavily charged with lime, as the following determinations 
in Table II will show: 1 

Table II. — Percentage of lime in freshly fallen hares, in terms of calcium car- 
bonate, or ground limestone. 



Kind of leaves. 



White oak . . 

Red oak 

Silver maple 



Percentage 
of lime. 



1.12 

3.08 
3.31 



Kind of leaves. 



Percentage 
of lime. 



Sugar maple . 

Tulip tree 

Virginia pine 



4.56 

5.06 

.16 



Soils containing such high percentages of lime as these leaves 
would be markedly alkaline, yet the leaves, as shown by the table on 
page 2, are strongly acid. It is evident from a consideration of both 
facts that the lime existing in the fresh leaves has gone into combina- 
tion with their acid substances to the full extent of its ability to neu- 
tralize them, and that the acidity recorded on page 2 represents the 
acid substances in the leaves in excess of the amount already neutral- 
ized by the lime. 

As the decomposition of the leaves progresses these excess acid 
substances are leached out or disorganized, the lime itself is released 
from its combinations, and a stage is reached where the lime is more 
(han sufficient in amount to neutralize the remaining acidity. The 
mass has become an alkaline leaf mold. This change from acidity to 
alkalinity is often hastened by the development through bacteria of 
ammonia or other substances having an alkaline reaction. 

The rapidity with which different kinds of leaves pass from the 
acid to the alkaline stage varies exceedingly. Leaves of silver maple 
in some tests have rotted so rapidly as to reach the alkaline state 
within a year. Red-oak leaves remain acid for several years, and pine 
leaves for many years. 

ACIDITY OF GREEN MANURES. 

Acidity determinations of several of the plants that are commonly 
plowed under for green manure give the following results, expressed 
in the weight of ground limestone that would be required per acre to 
neutralize a compact layer 6 inches in thickness. 

1 Those lime determinations wore made by Mr. .1. F. Broazeale, of the Bureau of Chem- 
istry, from duplicates of the same samples from which the acidity determinations on 
page 2 were made. 



AGRICULTURAL UTILIZATION OF ACID LANDS. 



Table III. — Acidity of green-manure crops to the acre, in terms of lime require- 
ment /a r acre. 



Crop. 


Acidity. 




Crop. 


Acidity. 


Ufalfa 


13 

9 

in 


Rye 


Tons. 

11 




Broom 




11 













The excessive acidity of these green manures at the time they are 
first plowed under may be more clearly appreciated when one consid- 
ers that the application of 2 to 3 tons of ground limestone per acre 
usually satisfies the requirements of an ordinary acid soil. The 
initial acidity of these green manures is thus shown to be several 
times that of an equal bulk of ordinary acid soil. In the process of 
decomposition, however, green manures, like the leaves already de- 
scribed, tend to pass from an acid to an alkaline state, but at rates 
which have not yet been determined. 

The lime requirement of green manures as given in Table III 
must not be understood as the amount of lime actually required to 
neutralize the acidity of a crop of these plants when plowed under. 
A compact 6-inch layer of green manure would never be used in actual 
practice, but a much smaller amount, as estimated in Table IV. This 
table gives the estimated weight of the dry crop per acre, roots as well 
as tops; the amount of lime in the crop, expressed in terms of ground 
limestone: and t lit' acidity, in terms of the additional amount of 
ground limestone required to neutralize the initial acidity. 

Table IV. — Weight, lime content, and acidity of green manures to the acre. 



Crop. 


Weight. 


Lime content. 


Acidity, expressed 
a.s lime require- 
ment. 


Alfalfa. . 


Tons. 


21 

2 

2 

1 


Pounds. 

L39 

131 
92 

11 
4 


Pounds. 

2*\7 




1 12 


Rye 


200 
178 




89 







INJURIOUS EFFECTS OF ACIDITY. 

Although science' can not be said to have demonstrated the full 
details of the various way- in which ordinary crops are injured by 
soil acidity, there is known to be one important chemical process 
which is suspended under acid conditions, namely, the transforma- 
tion of "unavailable" nitrogen into the form of nitrates. The 
nitrifying bacteria do not thrive in acid media. In consequence, 
those crops thai require their nitrogen in the form of nitrates suffer 



6 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 

from nitrogen starvation when growing in acid humus. For such 
crops the neutralization of the acidity by lime is of vital impor- 
tance, for not until this is done can the nitrogen of the humus, how- 
ever abundant, be changed into nitrates. Whatever other direct 
injurious effect acidity may have on crops, the fact that it checks 
the nitrification of humus is of itself sufficiently important and sig- 
nificant to justify all the investigation that the subject has received. 

SOURCE OF NITROGEN FOR ACID-LAND PLANTS. 

There is another phase of the acidity question. Many plants thrive 
in soils which are acid and which therefore theoretically can produce 
no nitrates. There are three possible methods by which these plants 
may secure their nitrogen : 

(1) Although a sample of soil when tested as a whole shows an 
acid reaction, there may exist in it innumerable minute tracts, sur- 
rounding particles of lime, where the reaction is alkaline and where 
nitrates are in process of manufacture. It is to be hoped that inves- 
tigators will find some means to determine the possibility of such 
a method of nitrogen nutrition in acid soils. 

(2) Many acid soils contain a large amount of nitrogen in the 
form of ammonia, and while hitherto scientific opinion has been much 
divided over the question whether ordinary crop plants can utilize 
ammonia nitrogen directly, without transformation by bacteria into 
nitrates, careful chemical investigation under such conditions as 
to eliminate the possibility of bacterial action should enable us to 
determine which of our crop plants can feed on ammonia nitrogen 
and which can not. Intelligent agriculture needs this information. 

(3) It is conceivable that a crop plant might utilize nitrogen that 
existed in organic form in the humus of the soil, having not yet 
reached the ammonia stage of decomposition. It is agreed by plant 
physiologists that ordinary plants, those bearing green foliage, are 
unable to do this. It is also agreed by plant physiologists that fungi 
not only can but habitually do use organic nitrogen. These two facts 
warrant the consideration of a remarkable partnership that exists 
between certain leaf-bearing plants and certain fungi, a partnership 
the significance of which has only recently begun to be appreciated by 
botanists and is almost unknown in agricultural literature. 

The subject is well illustrated in the blueberry. The possibility of 
the culture of this wild berry has been under investigation for several 
years, the experiments having now reached a successful conclusion. 1 

1 Experiments in Blueberry Culture, United States Department of Agriculture, Bureau 
of riant Industry, Bulletin 193, 1910; also Directions for Blueberry Culture, United 
States Department of Agriculture, Bureau of riant Industry, Circular 122, pages 3 to 11, 
1913. 



AGRICULTURAL UTILIZATION OF ACID LAN US. 7 

THE MVCORHIZAL FUNGI. 

It has been round thai the blueberry requires an acid soil, that it 
grows luxuriantly in a mixture of peat and sand containing nitrates 
in extremely minute quantities, if, indeed, they arc present at all. 
The plant bears upon its roots a fungus the microscopic threads of 
which lie partly on the outside of the root, but penetrate also into the 
living interior. While the experimental results can not as yet be 
regarded as furnishing an absolute proof, the evidence strongly indi- 
cates that the fungus takes up organic nitrogen from the abundant 
supply existing in the peat and delivers it to the plant in some 
available form. 

These mycorhizal fungi exist on the roots of many wild plants 
inhabiting acid peat. The extent to which they occur on the root- of 
cultivated plants that grow in acid soil is not yet known. It can 
hardly be doubted, however, that many such plants will ultimately 
be found to take their nitrogen through these fungi. Other acid- 
land plants will doubtless be found to possess the ability to use nitro- 
gen in the form of ammonia without the help of fungi. 

This outline of the probable mean- of nitrogen assimilation in 
acid-land plants prepare- the way for the following survey of crops 
adapted to acid soils. 

CROPS ADAPTED TO ACID SOILS. 

BLUEBERRY. 

The blueberry, to which allusion has already been made, gives 
every indication of adaptability to commercial culture, now that its 
soil requirements and it^ peculiarities of nutrition are known. The 
establishment of a blueberry-growing industry will mean the utiliza- 
tion of sandy, acid lands in the pine barrens of New Jersey and 
similar situations now regarded as almost usele-s agriculturally. 

CRANBERRY. 

The cranberry is an acid-land fruit. It has a root fungus similar 
to that of the blueberry and doubtless of the same importance to the 
welfare of the plant. The lands used for cranberry culture are of a 
special kind, with such an excess of moisture and acidity that in 
comparatively few instances would they have been used for any other 
agricultural purpose. 

STRAWBERRY. 

Tin' strawberry is now coming to be recognized a- a plant that 
thrives as well, if not a little better, in -oil- having an acid reaction. 
The grower who appreciate- this characteristic of the strawberry is 
relieved of (he expense of applying lime to his land unless required 
b}' other plants in his crop rotation. 



8 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 

BLACKBERRY, RASPBERRY, AND BLACKCAP. 

The blackberry, the American red raspberry, and the blackcap are 
found wild in acid soils and all thrive in cultivation in such land if 
the ground is well supplied with humus. 



The potato has long been recognized as yielding especially well 
when grown on a newly turned sod or on newly cleared land, condi- 
tions which are now recognized as productive of acidity as well as a 
later increase of humus. The potato, moreover, furnishes one phe- 
nomenon of special interest to acid-land agriculture. The potato 
scab, a disease which reduces the size of the tubers, injures their ap- 
pearance, and lessens their value, is controlled without difficulty if 
the soil reaction is acid. The disease is caused by a fungus known 
as Oosyora scabies, the growth of which is inhibited by acidity. 

SWEET POTATO. 

The sweet potato, the cultivation of which extends as far north as 
New Jersey, yields heavily in acid soils. In the South it is the 
standard vegetable on such lands. 



Rye is a cereal that grows almost as well on acid as on nonacid 
soils. It is the characteristic grain on the reclaimed acid heather 
lands of northern Europe. In the United States it is found par- 
ticularly useful as a cover crop on areas subject to washing in winter, 
whether the rye is later cut for hay, or plowed under for green 
manure, or harvested for its grain. 



As a grain for spring sowing, oats do well in acid soils, though this 
crop is not so acid tolerant as millet. It is often useful in rotations 
where the crop of the preceding summer can not be harvested early 
enough to permit the successful sowing of a winter cover crop like rye. 

MILLET. 

The different varieties of foxtail millet, including common millet, 
German millet, and Hungarian millet, are strongly acid tolerant. 
As they are also drought resistant and reach maturity in a remark- 
ably short period, they are useful for summer sowing in land tem- 
porarily vacant between the more important crops of a rotation. 

BUCKWHEAT. 

Buckwheat is well known as a pioneer crop on newly cleared timber- 
land. Its reputation also as a crop for worn-out lands is another 



AGRICULTURAL UTILIZATION OF ACID LANDS 9 

indication of its resistance to acidity, for such Lands are usually acid. 
If. however, the mineral food is actually insufficient and I here is no 
humus from which nitrogen can be extracted, one can not reasonably 
expect a heavy yield, even from buckwheat. The plant can with- 
stand acidity, but not starvation besides. A reasonable amount of 
humus, such as is easily provided by plowing under a good legumi- 
nous crop, will ordinarily result in heavy yields of buckwheat. 

REDTOP. 

The principal grasses of ordinary agriculture, notably bluegrass 
and timothy, do poorly in acid land. To this general rule, however. 
there is one notable exception, redtop. This grass often reaches a 
luxuriant development in markedly acid lands. The stem growth of 
redtop, however, is so light compared with that of timothy that it is 
not recommended as a substitute so far as the production of hay i- 
concerned, but. like bluegrass, its bottom growth is heavy and it 
makes an excellent pasture. 

CORN. 

Corn yields well under acid conditions if the soil is well provided 
with humus and the usual mineral nutrients. It may be regarded 
as a plant having a fair degree of acid tolerance. 



The carrot, as might readily be inferred from its common occur- 
rence as a weed in old and worn-out fields, is decidedly tolerant of 
acidity. It grows almost equally well in either type of soil. 

TIRNIP. 

The common turnip produces good though probably not maximum 
yields on acid land, differing in this respect from the rutabaga, or 
Swedish turnip, which yields well only in neutral or alkaline soils. 

LEGUMINOUS PLANTS FOR ACID SOILS. 

"While the crop plants thus far enumerated furnish material for 
such agricultural necessities as grain, grain hay. fodder, root crops. 
cover crops, pasturage, and small fruits, they do not supply the 
nitrogenous green manures which are necessary to the maintenance 
of soil fertility under most agricultural conditions and which are 
satisfactorily derived only from leguminous plants. Tt i> admitted 
that in acid-land agriculture red clover, the ordinary green-manure 
crop, is not available for this purpose. What, then, art' the legumi- 
nous plants which will produce in an acid -oil a heavy growth of 
tops equal in value to red clover for plowing ruder a-- green manure \ 
The answer is. cowpea and hairy vetch. Crimson clover, soy bean. 
lupine, and serradella are also useful me lei- certain condition-. 



10 BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 

COWPEA. 

For a century the cowpea, of many varieties, has been the chief 
leguminous crop of the Southern States, grown for hay, for its edible 
seeds, and as a green manure. Only recent ]y has its resistance to 
acidity been recognized. The experiment stations have carried the 
plant much farther north in the past few years, until now some of 
the varieties are in successful cultivation in Massachusetts, New 
York, and Michigan. Sometimes the yield of tops is so dense and 
heavy that only by the use of special attachments to the plow can 
the crop be turned under. 

SOY BEAN. 

The soy bean is of much more recent introduction into the United 
States than the cowpea. In its tolerance of acidity the soy bean 
probably equals the cowpea, and it has two points of superiority. 
It grows farther north and its yield of seed is much greater, often 
being as high as 30 bushels per acre. Some of the varieties have 
been grown with success as far north as New Hampshire, Ontario, 
and Wisconsin. The seed of the soy bean has one remarkable char- 
acteristic. It contains no starch, but about 35 per cent of nitroge- 
nous matter. Such a composition ought to give these beans a special 
value in rations for cattle. Within the climatic limits of its profit- 
able cultivation this plant may prove to be exceedingly valuable on 
the acid dairy farms of New England, where enormous sums are 
spent for the purchase of southern and western nitrogenous cattle 
feeds. 

HAIRY VETCH. 

Hairy vetch differs in one conspicuous feature from the cowpea 
and soy bean. Both these plants are sown in the spring or early 
summer and mature and die in the fall of the same year, but the 
hairy vetch is what is known as a winter annual. It is sown in late 
summer, germinates at once, passes the winter as a small plant, 
makes a heavy growth in the following spring, and matures its seed 
in early summer. It so closely accords in season with rye that the 
two form an ideal mixture when the rye is to be plowed under for 
green manure or cut for early hay. 

CRIMSON CLOVER. 

Crimson clover is a leguminous plant that does well in sandy soils 
from New Jersey southward. It appears to be tolerant of acidity 
and may come to be definitely recognized as a plant of this class. 
The seed is sown in late summer, becomes well established before 
winter, makes a luxuriant growth in early spring, and is ready for 
the scythe or the plow in May. 



AGRICULTURAL UTILIZATION OF ACID LANDS. 11 

Further experimentation will doubtless result in important addi- 
tions to this list. It is especially desirable that additional legumi- 
nous plants be found that are hardy far north and otherwise satisfac- 
tory in rotations. Lupine and serradella, both much employed in the 
great potato-growing districts of Pomerania and other portions of 
north Germany, ought to be useful in this country, but thus far they 
have not found favor, perhaps because of the poisonous qualities of 
lupine and the rather light yield of serradella. 

ACID-TOLERANT CROPS IN ROTATION. 

From the data already given, the farmer who desires to try an 
experiment in acid-land agriculture will be able to select the crops 
that will give him the rotation suited to the requirements of the par- 
ticular kind of agriculture in which he is engaged. Some of these 
crop plants are comparatively new and require special handling as to 
the best time and manner of sowing. "When grown for the first 
time the leguminous plants require soil inoculation with the special 
bacteria of their root tubercles. 

Rotations made up from the acid-tolerant crops described above 
have been very successful on some of the sandy, acid farms in Mary- 
land, a few miles northeast of Washington. 

The trees in one newly planted orchard of Grimes Golden apples 
have been kept in a remarkable condition of growth by one initial 
application of manure in the year of their planting, succeeded by the 
following rotation: In May the ground is sowed to cowpeas. These 
are plow T ed under in September and followed immediately by the 
sowing of rye mixed with hairy vetch. In the following May the 
mixed crop is plowed under. The same one-year rotation has been 
followed year after year. Under this treatment the soil, which has 
the appearance of almost pure sand, has become so fertile without 
the application of lime, commercial fertilizer, or manure that an 
occasional crop of cowpeas has been cut for hay without serious 
interference with the progress of the orchard. 

Another successful combination is a one-year rotation of corn and 
crimson plover by which a heavy yield of corn is produced every 
year without lime or fertilizer in a soil that looks almost like beach 
-and. The land, which is gently sloping, is ridged in contours at 
each interval of 2 feet in elevation, the corn rows being parallel to 
the contour next above them. The crop of crimson clover with the 
corn stubble is plowed under in April a little before corn-planting 
time. In August after the last cultivation of the corn the crimson 
clover is sown between the rows. The seeds germinate so readily 
that when broadcasted a light shower will start them oil'. If dry 
weather follows before they have had time to send their roots deep 



12 BULLETIN" 6, U. S. DEPARTMENT OF AGRICULTURE. 

enough to reach the permanently moist soil beneath the dry surface 
layer, the young plants promptly die. It is safer, therefore, either 
to sow the seed with a drill or to broadcast it during a heavy rain, 
which will beat the seed into the ground and at the same time fur- 
nish sufficient moisture to carry the young plants through the period 
of danger from drought. 

The turning under of heavy leguminous crops on these sandy soils 
restocks the land with humus and the humus decomposes to such a 
stage that a condition of partial or temporary alkalinity appears at 
times to have been reached, for good crops of even such nonacid 
plants as wheat and timothy are sometimes secured from these natu- 
rally acid lands after the treatment here described. 

BENEFICIAL EFFECTS OF SOIL ACIDITY. 

An actual beneficial effect from soil acidity is likely to be felt in 
another direction hitherto insufficiently recognized, namely, the con- 
trol of some of the fungous diseases of cultivated plants. Reference 
has already been made (p. 8) to the fact that the fungus causing 
the scab of the potato can not grow if the soil reaction is acid. 
Another example is furnished by the root-rot of the tobacco plant, 
caused by a fungus named Thielaina basicola. Briggs has shown 
that this disease is prevalent in tobacco plantations that have re- 
ceived excessive applications of lime or other alkaline fertilizers 
an 1 that it is readily controlled by the use of acid fertilizers. 

In Porto Rico the extension of the pineapple industry has been 
retarded by a disease known as chlorosis, the principal external 
mark of which is the yellowing of the foliage and the consequent 
poor nutrition of the plant. From - investigations by Gile and by 
Loew it appears that the yellow color of the leaves and the accom- 
panying weakness of the plant are due to the lack of iron, and that 
where the soil contains an excess of lime the organic acids which are 
needed to dissolve the iron of the soil are themselves neutralized 
and the iron, although present, is not available for absorption by the 
pineapple roots. 

In the upbuilding of the agriculture of the arid Western States 
certain diseases of plants have appeared which are commonly called 
by plant physiologists cases of "malnutrition." The causes of these 
maladies are unknown. The maladies themselves, however, are asso- 
ciated with pronounced alkalinity of the soil and they occur in 
plants that were native in humid regions where the soil varies from 
weak alkalinity to actual acidity. May it not be worth while for 
investigators to ascertain whether some of these mysterious " mal- 
nutrition " difficulties can not be remedied by an acid treatment of 
the soil? 



AGRICULTURAL UTILIZATION OF ACID LANDS. 13 

There is one other feature of the acid-soil question which merits 
the serious consideration of agriculturists. Recent investigators 
have shown that various fungi arc able to fix and feed upon the 
nitrogen of the atmosphere, just as do the bacteria of the clover root 
tubercles and certain free bacteria of alkaline and neutral soils. One 
Swiss investigator, Charlotte Ternetz, has isolated from acid soils 
several fungi in which this faculty not only occurs but is developed 
to a high degree of efficiency. It has not yet been fully demon- 
strated that true mycorhizal fungi possess this faculty of nitrogen 
fixation, but there is much evidence that they do. Should this be- 
come definitely established, agriculture must recognize in the my- 
corhizal fungi a direct and powerful means of adding to the store 
of available nitrogen, and the culture of mycorhizal plants in acid 
soils will have a significance far beyond the mere value of the crops 
produced by them. 

CONCLUSION. 

In closing this paper the writer desires to impress on agricultural 
investigators (1) that soil acidity is not always an objectionable 
condition which invariably requires an application of lime. (2) that 
under certain economic conditions a complete system of acid-land 
agriculture is practicable and desirable, and (o) that the extent to 
which our cheap eastern acid land- can be utilized with small appli- 
cations of lime, or under some conditions without its use. is a legiti- 
mate and important subject for detailed investigation, from which 
may reasonably be expected results of far-reaching economic im- 
portance. 



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